The original question was: Since snails live both in water and on land when did God make snails? As some land snails seem to go underwater, are snails at the sea side and the snails in my garden the same sort of thing, or can all snails do that?
Simon Terry has provided a very well illustrated answer to this question in his article Land and Sea Snails: Separate Creations.
Below is our summary below with a link to Simon’s full answer (PDF article) at the end.
The short answer is no, they are not the same. Land snails and sea snails are grouped together and called Gastropods, and they do have many similarities, but they also have some important differences, specially in how they breathe, that enable us to separate them into two distinct groups: the sea snails which breath under water (technically referred to as ‘Prosobranchs’), and those that live on land or freshwater and breathe air referred to as the ‘Pulmonates’).
One big difference between these two groups is the breathing apparatus. The word ‘Prosobranch’ is derived from the Greek proso meaning forward and branchia meaning gills. Sea snails therefore breathe underwater using a gill which can extract air directly out of the water. Whelks for example use their siphon (a soft tube like structure) to draw water into the mantle cavity, where the gill takes in oxygen and expels carbon dioxide.
Land and freshwater dwelling snails breathe with a lung, and take in air through an opening called a respiratory pore. Pond snails have a tube-like pore that they use like a snorkel to take in air when they are submerged. Land snails and slugs can partly submerge themselves in periods of drought, but prefer to escape water if they can. Some may even forage for food just beneath the water’s surface but must return to the land as their design and function is for terrestrial (land based) life.
There are also some other differences that show how each kind of snail is well designed for the habitat it lives in, such as their eyes, and whether they have an operculum (a lid for their shell opening). To learn more on how marine and land snails show good evidence of Biblical creation, and how the fascinating differences between them tell us they are separate kinds, see Simon Terry’s article Land and Sea Snails: Separate Creations. PDF here
For more information on snails see the question: What is the Snail Evolution project in British Schools, and what does the evidence show? Answer here.